Schoolfriends of a teenage girl killed in a frenzied stabbing hope the 20th anniversary of her unsolved murder will prompt information that may identify her killer.

Claire Tiltman, 16, was stabbed 40 times and left to die in a muddy alleyway as she walked to visit a friend on January 18 in 1993.

On Friday night, Claire's friends will carry candles as they retrace that fateful journey before a special memorial service in the church beside the murder scene. They want others to join them.

Emma Edwards, 35, said: "We were 15 and 16-year-old girls at the time and didn't really understand what had happened and the lasting impact it would have on us.

"Many of us have gone on to have our own families, but Claire was robbed of any of that.

We've always kept her memory alive, but this year we really hope we might persuade someone to come forward and tell the police what they know about the murder."

Claire, who was doing her mock GCSE exams, died after walking a mile from her home in Greenhithe, near Dartford, Kent.

Her parents made tearful appeals for information in the days after the murder of their only child and hoped they would see her killer jailed.

But they both died with that hope unfulfilled - her mother Lin, 56, in 2008 and her father 62-year-old Cliff last year.

Today, the family's modest home overlooking the QE2 bridge across the Thames is up for sale.

It stands empty and neglected, a testament to the enduring sadness of Claire's unsolved murder.

Over the years police took 1,700 statements, studied over 2,500 messages and examined 1,000 bits of physical evidence.

Seven suspects were questioned about the murder, but none was charged.

They included Robert Napper, the killer of Rachel Nickell on Wimbledon Common and Samantha Bissett, who was stabbed and mutilated at her home a few miles from where Claire died.

Local milkman Colin Ash-Smith was arrested, but released. He was later jailed for life in 1997 for a crazed knife attack on a young woman and the attempted rape and kidnap of another.

His mother Diane Ash-Smith said in a statement: "My family would like to express our sincere regret for the tragic loss of Claire, a young girl who had so much to look forward to. We also want to pass on our deepest sympathy to her friends and late family.

"I will emphasise that no one in my family , including my son Colin, has had any contact with the police in the last 15 years in any way. It is only the media who keeps bringing our family into the equation."

Detectives have never given up on the case and today scientists are applying new tests to the limited forensic evidence from the scene in the hope of a breakthrough.

Detective Superintendent Rob Vinson, from Kent Police, said: "Someone has the information we need, whether it's a memory of someone covered in blood, or acting strangely on that night, or simply an idea of the killer's identity.

"Claire had no chance of a future, her parents died without knowing why she was killed and who did it. It's not too late to give us information."

Anyone with information is urged to call the incident room on 01634 884010 or contact Crimestoppers, anonymously, on 0800 555 111.

The candlelit walk begins at 6pm on Friday opposite the Bull at Horns Cross, Greenhithe, and ends with a short service at St Mary's Church.